The present invention generally relates to work position error detecting apparatuses, and more particularly to a work position error detecting apparatus which is suited for use in a robot system such as a sealing robot system for sealing car bodies where there is a need to correct the position of a car body which is supplied as the work.
For example, in a painting robot system used in an automobile painting line, there is a need to detect the position of a car body which is supplied as the work, and feed back the detected position of the car body to a robot control part of the painting robot system so that the position of the car body can be corrected if the position of the car body is deviated from a reference position. In other words, a work position error detecting apparatus is required for detecting the deviation in the position of the work from the reference position.
As a previously proposed work position error detecting apparatus, there is a work position error detecting apparatus comprising four television cameras arranged below the automobile painting line. The car bodies on the automobile painting line respectively have four circular reference holes located at predetermined positions. The four reference holes may be holes which are originally provided in the car body for mounting certain parts or provided exclusively for the position detection. When the car body is positioned, the four television cameras pickup the corresponding reference holes which appear as oval holes in the picked up image because the television cameras respectively pick up the reference holes from an angle below the automobile painting line. The picked up image is processed so as to obtain data such as the center position, major axis, minor axis and inclination of each reference hole. The data is used to calculate the error in the position of the car body from the reference position in three dimensions, that is, the deviation along x, y and z axes and rotary deviation about the x, y and z axes which are often referred to as rolling, pitching and yawing.
However, the previously proposed work position error detecting apparatus has the following problems. Firstly, in order to process the picked up image, a computer which is used for control must process a large quantity of data. For this reason, it takes time to process the data, the response of the painting robot system is slow, and the production speed of the automobile painting line is slowed down thereby.
Secondly, when the television cameras are used to pickup the reference holes in the car body, the limit of the resolution is only in the order of 1% of the total field of vision. Hence, the accuracy with which the work position error is detected is unsatisfactory, and it is impossible to position the work with a high positioning accuracy. But in a sealing robot system for sealing car bodies, for example, it is essential that the work (car body) is positioned with a high positioning accuracy.